In modern technologies, electronic devices, such as computers, printers, scanners, modems, are getting more and more compatible and interchangeable. Also, supply voltages for such devices are decreasing.
FIG. 1 is a simplified block diagram of a prior art arrangement of device 10 with supply voltage V.sub.S1 (e.g., so-called rail-to-rail voltage) and device 20 having supply voltage V.sub.S2 .ltoreq.V.sub.S1. Convenient examples for the voltages are V.sub.S1 =5 volts and V.sub.S2 =3.3 volts. Device 10 may send signals 15 having temporarily a voltage V.sub.1 &lt;V.sub.S1 to device 20. Second device 20 must accommodate V.sub.S1. Device 20 receives signal 15 by voltage divider 30 serving as a signal conversion circuit. Voltage divider 30 has resistors 31 and 32 serially coupled to common reference 35 of circuits 10 and 20. With magnitudes R.sub.A and R.sub.B of resistors 31 and 32, respectively, voltage divider 30 provides an intermediate voltage V.sub.2 : ##EQU1## Voltage divider 30 consumes a current I: ##EQU2## Such a current leads to power consumption in device 10 which is not convenient. In other words, circuit 10 must have enough drive capability to accommodate a low input impedance of the conversion circuit (e.g., voltage divider 30) in device 20. The impedance of circuit 20 should be high, not low. A configuration as in FIG. 1 is especially inconvenient when circuit 10 is a battery powered interface whose battery is discharged by current I.
The present invention seeks to provide an improved signal conversion circuit which mitigates or avoid the above mentioned and other disadvantages and limitations of the prior art.